linux-kernel - Re: 3.9-rc5: Encountedred INFO: rcu_sched self-detected stall on CPU due to 09a9f1d27

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Message-ID: <20130520202328.GG2739@redhat.com>
Date:	Mon, 20 May 2013 16:23:28 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 3.9-rc5: Encountedred INFO: rcu_sched self-detected stall on CPU
 due to 09a9f1d27

On Mon, Apr 29, 2013 at 09:29:52AM -0400, Vivek Goyal wrote:
> On Mon, Apr 29, 2013 at 01:57:18AM -0700, Michel Lespinasse wrote:
> > On Mon, Apr 15, 2013 at 6:27 PM, Hugh Dickins <hughd@...gle.com> wrote:
> > > On Mon, 15 Apr 2013, Michel Lespinasse wrote:
> > >> sys_brk() passes the length as the difference of two page aligned addresses, so it's fine. But vm_brk() doesn't - it calls do_brk() which page aligns the length, but then vm_brk passes the unaligned length to mm_populate().
> > >>
> > >> What do you think of the following ? len is already a PAGE_SIZE multiple when called from sys_brk()...
> > >
> > > Yes, that's good.
> > >>
> > >> diff --git a/mm/mmap.c b/mm/mmap.c
> > >> index 0db0de1c2fbe..6af8b0d1c7db 100644
> > >> --- a/mm/mmap.c
> > >> +++ b/mm/mmap.c
> > >> @@ -2557,10 +2557,6 @@ static unsigned long do_brk(unsigned long addr, unsigned long len)
> > >>       pgoff_t pgoff = addr >> PAGE_SHIFT;
> > >>       int error;
> > >>
> > >> -     len = PAGE_ALIGN(len);
> > >> -     if (!len)
> > >> -             return addr;
> > >> -
> > >>       flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
> > >>
> > >>       error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
> > >> @@ -2643,6 +2639,10 @@ unsigned long vm_brk(unsigned long addr, unsigned long len)
> > >>       unsigned long ret;
> > >>       bool populate;
> > >>
> > >> +     len = PAGE_ALIGN(len);
> > >> +     if (!len)
> > >> +             return addr;
> > >> +
> > >>       down_write(&mm->mmap_sem);
> > >>       ret = do_brk(addr, len);
> > >>       populate = ((mm->def_flags & VM_LOCKED) != 0);
> > 
> > Vivek - what should I do with this change ? Do you want to take it as
> > part of your series, or should I push to Linus/Andrew ?
> > 
> > All vm_brk calls are in elf and aout loaders, so I don' t think we can
> > hit the issue without your changes. Still, it may be good to make
> > vm_brk robust anyway.
> 
> Hi Michel,
> 
> Thanks for the fix. Sorry, could not respond earlier as I was away from
> work.
> 
> This patch did fix the issue for me. I think it is a good idea to push
> this fix to Andrew irrespective of my changes. My series is in RFC phase
> and there are no guarantees whether patches will be accespected or not.
> 
> So please go ahead and send this fix to andrew for inclusion. 

Hi Michel,

So are you planning to push this patch upstream?

Vivek
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